Different number range for same employee group during pernr creation

We replicate employee master data from successafactors to ERP (SAP system) into infotype DB. We are using decoupled infotype framework classes for same.

During a new hire pernr in ERP is mapped to successfactor person-id-external.

We have a customer scenario, where they have an employment change in SF (eg: Contract to regular employee).

When employee is initially hired as an contract employee, new pernr in ERP will be mapped to person-id-external number. Then later contract employee is terminated and rehired as an regular employee, in ERP new pernr should be created for same but since they can't use person-id-external from SF now, they want system to generate a unique pernr here.

Since we have already defined the person-id-external from SF as 'external' number range (PA04 transaction).

But for later scenario, where system has to generate unique number for 2nd employment, how can that number range be defined ?.

Tricky thing here is, Org details in 2nd employment in above example can be the org details for 1st employment for some other employee.

How can i use the number range or NUMKR feature in above scenario to generate unique pernr?.